The Student Room Group

Geometry in curved space

My general relativity notes start by running through examples of calculating the circumference and area of discs on a sphere, and they state that the area of a disc on a sphere in spherical polar (so a dome shape) is equal to the integral over phi and theta of the square root of the determinant of the Euclidean metric for polar coordinates. Why is the determinant used? Where does this come from? Thanks

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